sky2: fix VLAN receive processing (resend)

The length check for truncated frames was not correctly handling
the case where VLAN acceleration had already read the tag.
Also, the Yukon EX has some features that use high bit of status
as security tag.

Signed-off-by: Pierre-Yves Ritschard <pyr@spootnik.org>
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>